High efficiency variable voltage supply

ABSTRACT

Aspects of the present disclosure are generally directed to a power supply for generating an output supply voltage. The power supply generally includes a variable voltage supply configured to generate an intermediate supply voltage based on a reference signal, a correction circuit configured to generate an error signal based on the output supply voltage or the intermediate supply voltage, and a combiner configured to combine the intermediate supply voltage and the error signal to provide the output supply voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 15/170,217 with a filing date of Jun. 1, 2016, which is aContinuation of U.S. patent application Ser. No. 14/223,494 with a U.S.filing date of Mar. 24, 2014, which is a Continuation of U.S. patentapplication Ser. No. 13/169,771 with a U.S. filing date of Jun. 27,2011, which is a Continuation of U.S. patent application Ser. No.11/574,218, with a U.S. filing date of Aug. 2, 2007, which is a 371filing of PCT/GB2005/003318, filed on Aug. 25, 2005 which in turn claimspriority to British Application Number 0418991.6, filed on Aug. 25,2004, all of which are assigned to the assignee of the presentapplication and hereby expressly incorporated by reference herein intheir entireties.

BACKGROUND

Field of the Invention

The present invention relates to control of a supply voltage level, inan arrangement in which the supply voltage is variable to track areference level, which reference level may represent a signal to beamplified.

Background of the Invention

Modern communications systems often employ linear modulation schemesthat exhibit high peak to average power ratios to achieve high capacity.Signals subjected to such modulation have a wide dynamic range,infrequently achieve peak levels, and frequently operate below peaklevels. To provide linear amplification for signals subjected to suchmodulation, traditional radio frequency (RF) amplifier architecturesneed to be significantly backed-off. This generally results in poorefficiency.

A number of techniques exist to improve efficiency based on supplyvoltage. Notable amongst these supply voltage based efficiencyenhancement schemes are those of envelope tracking and envelopeelimination and restoration.

These two techniques improve efficiency by dynamically adjusting ortracking the supply to the amplifier device in harmony with the envelopeof the modulation signal to be amplified. When applied to an amplifierstage, the dynamic adjustment of the supply alters the drain supply orbias of the amplifier. This results in high final stage efficiencies.

At least three problems exist in implementing such dynamic supplyadjustment techniques. Firstly the need to modulate the supply mayrequire tracking bandwidths of three to four times the modulationbandwidth of the signal to be amplified, which must be generatedefficiently. Secondly, any noise or distortion in the supply to theamplifier will be modulated up to the carrier frequency resulting inunacceptable out-of-band spectral emissions. Finally, the supplytypically requires a high output voltage dynamic range and is typicallyrequired to deliver a high peak to average power ratio.

As a result a supply voltage modulation source not only needs to beefficient, but must also have a tracking response which is substantiallyaccurate; has a high slew rate and peak power; and produces distortionthat is either small or bandwidth constrained and predictable.

When applied to high power broadband systems such as multi-carrier WCDMA(wideband code division multiple access), prior art attempts to addressthis problem using either Class-S modulators (pulse width modulation) orClass-G modulators (switched supply) exhibit unacceptable performancedue to insufficient tracking bandwidth, excessive switching losses, orunacceptable distortion characteristics.

It is an aim of the invention to provide an improved technique whichaddresses one or more of the above-stated problems. In particular it isan aim of the invention to provide an improved supply architecture,which offers improved or optimised efficiency.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention there is provided apower supply stage, comprising: selection means for selecting a powersupply voltage from a high efficiency variable voltage supply independence on a reference signal; adjusting means for receiving theselected power supply voltage, and adapted to generate an adjustedselected power supply voltage tracking the reference signal independence thereon.

Further in accordance with the first aspect of the invention there isprovided a power supply stage, comprising: generating means forgenerating a power supply voltage from a high efficiency variablevoltage supply in dependence on a reference signal; adjusting means forreceiving the generated power supply voltage, and adapted to provide anadjusted generated power supply voltage tracking the reference signal independence thereon.

The generating means may select a power supply voltage from a pluralityof discrete levels of voltage supply. The generating means may be aselection means. The generating means may provide a power supply voltagebased on an approximate continuous selection.

The output efficiency of the high efficiency variable voltage supply maybe greater than 0.7.

The power supply stage may further comprise a lower efficiency supplyfor supplying the adjusting means. The output efficiency of theadjusting means may be greater than 0.4.

The reference signal may comprise an input waveform representing adesired supply voltage level. The high efficiency variable voltagesupply may generate an intermediate supply voltage level.

The adjusting means may include a correction element for generating anerror level representing an error between a desired voltage supply leveland an output supply voltage level.

The power supply stage may be adapted to maximise the efficiency of thehigh efficiency variable voltage supply, whilst maintaining a lowpeak-to-average ratio for the error level. The power supply stage may beadapted to maximise the efficiency of the high efficiency variablevoltage supply, whilst maintaining a low slew rate for the error level.A ratio of peak error signal to peak output signal is preferablymaintained at less than 0.5. A ratio for peak error signal slew rate topeak output signal slew rate is preferably less than 1.5.

The error level may be generated in dependence on the supply voltagelevel fed back from an output of the supply voltage stage.

The error level may be a voltage level, an energy level, or a powerlevel.

The error level may be generated in dependence on a prediction of thesupply voltage level at an output of the supply voltage stage. Theprediction of the supply voltage level may be at least partly determinedin dependence on the intermediate supply voltage level.

The adjusting means may include a combiner for combining the error levelwith an intermediate supply voltage level to generate the output supplyvoltage level. The intermediate supply voltage level may be adjusted byadding or removing voltage or energy.

The combiner may be adapted to sink energy, source energy, or sinkenergy and source energy, in dependence on the error level. The combinermay be adapted to sink energy from, source energy to, or sink energyfrom and source energy to, the output of the high efficiency variablevoltage supply.

The adjusting means may be configured to source energy to allowadjustment of the output supply voltage level above the intermediatesupply voltage level. The adjusting means may be configured to sinkenergy to allow adjustment of the output supply voltage level below theintermediate supply voltage level. The adjusting means may be configuredto source and sink energy to allow adjustment of the output supplyvoltage level above and below the intermediate supply voltage level.

The intermediate supply power may be greater than an error power. Theratio of the error power to the intermediate supply power may be muchless than 1. The ratio of the error power to the intermediate supplypower may be less than 0.4.

The power associated with the signal providing the intermediate supplyvoltage level may be greater than the power associated with the signalproviding the error level.

The correction element may be configured to receive a continuous supplymodulation. The correction element may be configured to receive a supplyswitched between pluralities of supplies. The switched supply may be aClass-G or Class-H supply.

The high efficiency variable voltage supply may be optimised forefficiency at the expense of accuracy. The high efficiency variablevoltage supply may be further optimised for transient response at theexpense of accuracy.

The correction element of the adjusting means may be optimised toprovide accurate error tracking. The correction element of the adjustingmeans may be further optimised to deliver high peak to mean output powerwith good efficiency. The correction element of the adjusting means maybe a linear Class-G amplifier having multiple power supplies. Thecorrection element of the adjusting means may be a linear Class-Hamplifier having multiple power supplies.

There may be further provided a feedback from the high efficiencyvariable voltage supply to the selection means. There may be furtherprovided a feedback from an output of the power supply stage to theselection means.

The selection means may include tracking means.

In a second aspect the invention provides a power supply stage having anoutput supply voltage level, comprising: a variable voltage supply,adapted to generate an intermediate supply voltage level in dependenceon an input waveform representing a desired output supply voltage level;a correction element, adapted to generate an error level representing anerror between the actual output supply voltage level the desired supplyvoltage level; and a combiner for combining the error level and theintermediate supply voltage level to provide the output voltage supplylevel.

The variable voltage supply may include a high efficiency supply stageand the correction element includes a lower efficiency supply stage.

The variable voltage supply may include a supply stage for generating anoutput signal having efficiency greater than 0.7, and the correctionelement includes a supply stage for generating an output signal havingefficiency greater than 0.4.

The output signal of the correction element may have a lower efficiencythan an output signal of the supply stage.

The intermediate supply voltage signal may be associated with anintermediate power level and the error level signal may be associatedwith an error power level, the intermediate power level being muchgreater than the error power level.

The ratio of the error level to the intermediate supply voltage levelmay be less than 0.4. The output of the stage may have an efficiency ofgreater than 0.7. The ratios may be power or voltage ratios.

The efficiency of the variable voltage supply may be maximised, whilstjointly minimising the peak-to-average ratio of the error level and theslew rate of the error level. A ratio of peak error signal to peakoutput signal may be maintained at less than 0.7, and a ratio for peakerror signal slew rate to peak output signal slew rate may be maintainedat less than 1.5.

The output of the stage may provide a power supply to a radio frequencyamplifier.

In an aspect the invention provides a method of controlling a powersupply stage, comprising: selecting a power supply voltage from a highefficiency variable voltage supply in dependence on a reference signal;receiving the selected power supply voltage, and adjusting the selectedpower supply voltage by tracking the reference signal in dependencethereon.

The output efficiency of the high efficiency variable voltage supply maybe maintained as greater than 0.7.

The method may further comprise providing a lower efficiency supply forsupplying the adjusting means. The output efficiency of the adjustingmeans may be maintained as greater than 0.4.

The method may further comprise providing, as the reference signal, aninput waveform representing a desired supply voltage level.

The method may further comprise generating an intermediate supplyvoltage level.

The method may comprise generating an error level representing an errorbetween a desired voltage supply level and an output supply voltagelevel.

The method may further comprise combining the error level with theintermediate supply voltage level to generate the output supply voltagelevel.

The intermediate supply power may be maintained greater than errorpower.

The method may comprise maintaining the ratio of the error power to theintermediate supply power as much less than 1.

The ratio of the error power to the intermediate supply power may bemaintained as less than 0.4.

The method may further comprise maintaining the power associated withthe signal providing the intermediate supply voltage level as greaterthan the power associated with the signal providing the error level.

The method may further comprise minimising the peak amplitude of theerror level. The method may further comprise maintaining a ratio of peakerror level to peak output level of less than 1. The ratio of the peakerror level to peak output level may be maintained at less than 0.7.

The method may further comprise minimising the slew rate of the errorlevel. The ratio of the peak slew rate of error level to the peak slewrate of the output level may be maintained as less than 1.5.

In another aspect there is provided a method of controlling a powersupply stage having an output supply voltage level, comprising:generating an intermediate supply voltage level in dependence on aninput waveform representing a desired output supply voltage level;generating an error level representing an error between an actual outputsupply voltage level the desired supply voltage level; and combining theerror level and the intermediate supply voltage level to provide theoutput voltage supply level.

The invention may be considered to consist of a high efficiency, highaccuracy, tracking supply comprising one or more of the followingelements or functionalities: a high efficiency variable output supplyhaving the ability to track significant transients of the input(reference) waveform with coarse accuracy, distortion or limitedresponse; an active correction element to remove any error between thevariable supply output and desired output; a tracking control element tostimulate the high efficiency supply and supply correction elements inresponse to the reference waveform; such feedback and control loops asrequired to ensure that the resulting supply provides a faithfulrepresentation of the reference waveform.

According to embodiments of the invention there is provided a powersupply stage, comprising: reference means for providing a referencesignal representing a desired power supply voltage; election means forselecting an approximate power supply voltage in dependence on thereference signal; adjusting means for receiving the selected powersupply voltage and the reference signal and adapted to generate anadjusted selected power supply voltage tracking the reference signal independence thereon.

The power supply stage may be for an amplifier, the reference signalrepresenting the envelope of an input signal of said amplifier. Theadjusting means may include linear amplifier. The selected power supplyvoltage may have the minimum absolute difference between said powersupply voltage and the reference signal level.

The linear amplifier may be connected to amplify the difference betweenthe reference signal and a representation of the selected power supplyvoltage. The adjusting means may include means for summing the amplifieddifference with the selected supply voltage.

The representation of the selected power supply voltage may be the powersupply voltage itself. The representation of the selected power supplyvoltage may be the adjusted selected power supply voltage. The adjustedselected supply voltage may be the output of the power supply stage.

The adjusting means may comprise a plurality of cascaded correctioncircuits. The adjusting means may comprise two or more cascadedcorrection circuits.

According to embodiments of the invention the present invention providesa radio frequency amplification stage comprising: an amplifier forreceiving an input signal to be amplified and a power supply voltage;and a power supply voltage stage for supplying said power supplyvoltage, comprising: means for providing a reference signal representingthe envelope of the input signal; means for selecting an approximatevoltage level in dependence on the reference signal; and means forgenerating an adjusted selected power supply voltage, comprising alinear amplifier for amplifying a difference between the referencesignal and one of the selected supply voltage level or the adjustedselected supply voltage level, and a summer for summing the amplifieddifference with the selected supply voltage to thereby generate theadjusted supply voltage.

The means for generating an adjusted selected supply voltage may furthergenerate a further adjusted supply voltage and further comprises an RFamplifier for amplifying a difference between the reference signal andone of the adjusted supply voltage or the further adjusted supplyvoltage, and a summer for summing such amplified difference with theadjusted supply voltage to thereby generate the further adjusted supplyvoltage.

One of the adjusted supply voltage or further adjusted supply voltagemay form the supply voltage to the amplifier.

According to embodiments of the invention the present invention providesa method of controlling a power supply stage, comprising: providing areference signal representing a desired power supply voltage; selectingan approximate power supply voltage in dependence on the referencesignal; generating an adjusted selected power supply voltage trackingthe reference signal in dependence on the selected power supply voltageand the reference signal.

The reference signal may represent the envelope of an input signal to anamplifier, the power supply stage providing a power supply to saidamplifier. The difference between the reference signal and arepresentation of the selected power supply voltage may be amplified.The amplified difference may be summed with the selected supply voltageto form the adjusted supply voltage. The difference between thereference signal and a representation of the adjusted power supplyvoltage may be RF amplified.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described by way of example with reference tothe accompanying Figures, in which:

FIG. 1 illustrates an envelope tracking supply voltage variationtechnique in the prior art;

FIG. 2 illustrates a supply architecture in accordance with theprinciples of the invention;

FIG. 3 illustrates the improvement in the envelope tracking supplyvoltage technique in accordance with the invention;

FIG. 4 illustrates efficiency improvements obtained in accordance withthe invention;

FIG. 5 illustrates a supply architecture in accordance with a firstembodiment of the invention; and

FIG. 6 illustrates a supply architecture in accordance with a firstembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is described herein by way of particular examples andspecifically with reference to a preferred embodiment or embodiments. Itwill be understood by one skilled in the art that the invention is notlimited to the details of the specific embodiments given herein. Inparticular the invention is described herein by way of reference to asupply architecture for supplying a radio frequency (RF) amplificationstage. However more generally the invention may apply to any arrangementwhere it is necessary to provide a variable voltage level tracking areference level.

Reference is first made to FIG. 1, which illustrates the concept of anenvelope tracking supply voltage, and the problems associated therewith.The problem is described in relation to a variable voltage supply for aradio frequency (RF) amplifier, the voltage supply being varied to trackthe RF input signal to be amplified. By way of example, it is assumedthat the variable voltage supply is provided by a switchable voltagesupply, as known in the art.

Referring to FIG. 1, there is illustrated a plot of voltage againsttime. On the voltage axis, there is illustrated four specific voltagelevels V₁-V₄ corresponding to the voltage levels provided to a supplyvoltage selection block. It should be noted that the provision of fourvoltage supplies is illustrative, and any supply voltage selection blockmay in fact be provided with more or less voltage supplies in accordancewith implementation requirements.

Curve 106 of FIG. 1 illustrates the voltage envelope of an RF inputsignal to an RF amplification stage. The dash line curve 104 illustratesthe idealised voltage supply envelope for such an RF input signal. Ascan be seen, the dash line curve 104 tracks the RF input signal envelope106 to provide an idealised power supply voltage level for the inputsignal voltage level. As such, the idealised power supply voltage levelavoids any wasted power and consequently is very efficient.

The stepped trace 108 illustrates a typical actual voltage supply levelto an RF power amplifier based on a switched supply voltage of fourlevels, reflecting performance typical in prior art implementations. Asthe envelope 106 of the RF input signal reaches ones of the voltagelevels V₁-V₄, the supply voltage is appropriately switched. As cantherefore be seen from FIG. 1, the supply voltage 108 steps between thefour supply voltage levels, such that it is above the RF input signal atall times. As such, the supply voltage level to the RF amplifier isfrequently excessive. The hatched area 110 in FIG. 1, for example,represents wasted energy, corresponding to supply voltage levels abovethe idealised level, which are consequently unnecessary. As illustratedby the hatched area 110, the stepped supply voltage implementation ofthe prior art is generally significantly less efficient than theidealised solution.

A further limitation of the architecture of FIG. 1 is illustrated byreference numerals 111 and 113 in FIG. 1. It can be seen, as denoted byreference numerals 111 and 113 that some oscillation may be included inthe stepped trace 108. Parasitic inductance and capacitance of thecircuit implementation may result in output transients that produceundesirable modulation of the supplied RF amplification stage. As thenature of these transients is broadband and generally unknown theycannot be easily mitigated by techniques that pre-correct the modulationinformation. This lack of accurate control over the supplied voltagelimits the supplies usefulness in RF amplification.

Further problems associated with typical prior art arrangements arediscussed in the introductory portion of the specification.

A preferred supply architecture in accordance with the preferredprinciples of the invention, which provides an improved performance overthe prior art performance illustrated in FIG. 1, is illustrated in FIG.2. The architecture of FIG. 2 represents an accurate tracking supply,exhibiting high efficiency.

Referring to FIG. 2, the supply architecture is generally designated byreference numeral 202 and includes a tracking control block 206, a highefficiency variable supply block 204, an active supply correction block208, and a combiner 222.

The tracking control block receives an input on line 216. The trackingcontrol block 206 provides an output on line 210 to an input of the highefficiency variable supply 204, and an output on line 214 to an input ofthe active supply correction block 208. The high efficiency variablesupply block provides an output on line 212 to a first input of thecombiner 222. The active supply correction block 208 provides an outputon line 226 to a second input of the combiner 222. The combinergenerates an output on line 220, which forms an output supply voltage ofthe supply architecture.

Certain optional connections are also shown in FIG. 2. An optionalfeedback connection 224 is shown connecting the output of the highefficiency variable supply block 104 on line 212 to an input of thetracking control block 206. An optional feedback connection 218 is shownconnecting the output of the combiner on line 220 to the input of thetracking control block 206 and to an input of the active supplycorrection block 208. Such optional connections are preferably employedto help ensure the resulting supply is a faithful representation of thereference waveform, as discussed with reference to FIG. 5.

It should be noted that the architecture of FIG. 2 is illustrative. Anyelement thereof may include a plurality of elements or components. Anyconnections may represent a plurality of connections, such as multiplesignal lines, or a single connection, in dependence on a givenimplementation.

The input on line 216 represents the signal which the supply voltage isto track, and may be the actual signal to be tracked. The signal on line216 is preferably a radio frequency (RF) envelope waveform, possiblyderived from a signal to be amplified by an amplifier to which thesupply architecture 202 provides a supply voltage.

The tracking control block 206 may receive on the input line 216 anactual signal to be amplified by an amplifier for which the supplyarchitecture 202 provides a supply voltage. The tracking control block206 may include an envelope detector, and provide the envelope of theinput signal on line 216 on its output line 210, for use by the highefficiency supply block 204. The envelope on line 210 may then be usedby the high efficiency supply to determine a voltage level to be appliedon line 212. The output line 210 may, in an embodiment, comprise aplurality of lines, representing a plurality of possible switchselections for the high efficiency variable supply block 204, forexample where the high efficiency variable supply block is a device forswitching between discrete voltage levels.

The tracking control block 206 also provides a reference signal on line214 to the active supply correction block 208. The reference signal maybe the output of an envelope detector, but more generally may beconsidered to be representative of the signal to which the supplyvoltage generated by the supply architecture 202 is to track.

The outputs of the tracking control block on lines 210 and 214 may bethe same signal, the same signal with different delays, different ormodified versions of the same signal, or different signals. The trackingcontrol block is configured to supply to each of the high efficiencyvariable supply block 204 and the active supply correction block 208 anysignal necessary for the operation of such blocks in accordance with theprinciples of the invention

The high efficiency variable supply voltage block 204 is preferablyoptimised to have high supply efficiency at the expense of trackingaccuracy. This trade-off is further discussed herein.

The high efficiency variable supply block 204 provides an intermediatesupply voltage level at its output on line 212, which corresponds towhat is typically referred to as a coarse or inaccurate tracking of theinput signal on line 216. The high efficiency variable supply ispreferably of a switching type and may be implemented in any one of anumber of ways. For example, there may be provided a number of fixedsupply voltage levels which can be switched between, such that theintermediate supply voltage level on line 212 corresponds to one of suchfixed supply voltage levels.

In alternative embodiments, the high efficiency variable supply block204 may include means for combining ones of a plurality of fixed supplyvoltage levels to generate the intermediate voltage supply level on line212. The intermediate voltage supply level on line 212 may therefore bebased on one or more selected supply voltage levels.

In a further embodiment, the high efficiency variable supply block 204may be implemented as a poly-phase Class-S stage, for example using asingle input supply and multiple tuned combining networks selectedeither singularly or in combination to achieve a high dynamic range.

The high efficiency variable supply voltage block is not limited tobeing one of a switching type. Any technique for providing a variabletracking voltage may be used, whether such technique employs switchingor otherwise.

In general, therefore, the high efficiency variable supply block 204 maybe considered to be a generating means for generating a power supplyvoltage from a high efficiency variable voltage supply in dependence ona reference signal provided thereto. Such a generating means iseffectively a selection means, for selecting a supply voltage in adiscrete or continuous manner, i.e. by selection between discrete valuesor by providing a continuous output which varies.

The active supply correction block 208 operates to provide an errorlevel, or error signal, on line 226, which represents the error betweenthe intermediate supply voltage level on line 212 and an idealised ordesired supply voltage level. This error may be represented as an energylevel of a voltage level, for example. The idealised supply voltagelevel is based on the level of the signal on line 216, and representedto the active supply correction block 208 as the reference signal online 214.

In a practical implementation, in order to generate the error signal theactive supply correction block 208 must be able to compare the idealisedsupply voltage level to a supply voltage level currently beinggenerated. This may be achieved by feedback or feedforward means, indifferent embodiments. This is discussed in more detail below withreference to FIGS. 4 and 5. Thus the reference signal on line 214 mayprovide feedforward information as well as the reference signal, orfeedback information may be provided via connection 218. Other methodsfor providing feedback or feedforward prediction may be used.

It should be noted that the idealised supply voltage level may notnecessarily be the actual voltage level of the signal on line 216, butmay be an offset level from that signal level. Hence the idealisedsupply voltage level may be considered to be based on or derived fromthe level of the signal on line 216, and not necessarily be the actualsignal level itself.

The combiner 222, which is preferably a low loss combiner, combines theintermediate supply voltage level on line 212 with the error level,which may be a voltage level, on line 226, and generates an outputsupply voltage level on line 220. The output supply voltage level online 220 is thus the intermediate supply voltage level, or coarsevoltage level, on line 212, with an error presented on line 226 removedtherefrom. As the error approximates to the difference between theintermediate voltage level and the idealised supply voltage level, theoutput supply voltage level more closely approximates to the idealisedsupply voltage level.

Combining of the supply voltage level on line 212 with the error levelon line 226 is preferably not restricted to absolute addition. The errorlevel on line 226 may add, subtract or add and subtract from the supplyvoltage level on line 212. The active supply correction block 208 maythus be adapted, for example, to source, sink or source and sink energyto allow such correction.

An adjusting means is provided by one or all of the tracking controlblock 206, the active supply correction block 208, and the combiner 222.The adjusting means receives the power supply generated by the highefficiency variable supply 204, and is adapted to provide an adjustedgenerated power supply voltage which tracks a reference signal. Suchadjusting means is effectively a voltage adjustment block, operated inaccordance with the principles of preferred embodiments of the inventionto adjust the intermediate supply voltage level on line 212, to providean adjusted output supply voltage level on line 220.

Referring to FIG. 3, there is illustrated the efficiency improvementachieved in accordance with the invention and its embodiments. Thestepped trace 302 illustrates the voltage supply generated by, in anembodiment, the switched supply voltages of the high efficiency variablesupply block 204. The supply voltage 302 provided by a supplyarchitecture arranged in accordance with the principles of the inventiontracks above and below the envelope 306.

The supply architecture in accordance with the invention is configuredto approximately follow, as closely as possible, the envelope of areference signal without incurring additional energy dissipation, asrepresented by hatched area 208 in FIG. 1.

The embodiments of the invention result in an actual supply voltagelevel 302 which more closely follows an idealised supply voltage level304, resulting in improved efficiency and an intermediate supply voltagelevel which is more closely aligned to the idealised voltage 304.

The difference between the idealised supply voltage level 304 and theintermediate supply voltage level 302 represents the error signal 226that is required to be contributed by the active supply correctionblock. This signal is by preference minimised. The error signal iscombined with the intermediate supply voltage level 302 to produce asubstantially accurate representation of the idealised supply voltage304 at the supply output.

The supply architecture of the invention and embodiments thereof,provide a particularly improved solution in which the supply voltagelevel closely tracks the idealised supply voltage level and, as shown inFIG. 3, minimises wasted energy, and thereby maximises efficiency.

The tracking depicted in FIG. 3 is illustrative. In accordance with therequirements of a given implementation, the intermediate supply levelmay be adapted to track above the reference signal, above and below thereference signal, or below the reference signal. The appropriate methodis chosen in accordance with an optimisation of the supply efficiency asdescribed herein.

The active supply correction block 208, as discussed hereinabove, may beconfigured to source energy, sink energy, or source and sink energy. Tooptimise the efficiency of the correction operation, it is preferablethat the active supply correction returns at least a portion of anyenergy sunk to a reservoir (not shown) for future use. The provision ofsuch reservoirs is known in the art.

The invention advantageously provides a high bandwidth, high accuracyvariable power supply that exhibits a high power conversion efficiency.Further advantageously, and significantly, the supply provides a largeoutput voltage dynamic range and high peak to average power deliverycapability.

Prior art techniques have illustrated the difficulty in achieving asupply with high power conversion efficiency when delivering highbandwidth, dynamic range and accuracy. Architectures have achieved highbandwidth and/or dynamic range at the expense of accuracy, or accuracyat the expense of bandwidth and/or dynamic range, but no solutionaddresses all three requirements at the same time.

The supply architecture 202 overcomes the accuracy limitations ofprevious high bandwidth and/or high dynamic range supply architecturesby utilising a correction means of lesser constraint. Neither the highefficiency variable supply 204 nor the adjustment means fulfil all thedesired constraints individually. However they are arranged, inaccordance with embodiments of the invention, such that in combinationall of the desired constraints are met.

The optimisation of the supply architecture 202 in accordance with theembodiments of the invention is now described in further detail.

The voltage waveforms at the combiner 222 of FIG. 2 can be representedby the expression:

e(t)=r′(t)−p(t)  (1)

where e(t) denotes the error voltage level on line 226, p(t) denotes theintermediate supply voltage level on line 212, and r′(t) denotes theoutput supply voltage level on line 220.

The associated output powers (over a time interval T) can be expressedas follows:

$\begin{matrix}{{E = {\int_{0}^{T}{\frac{{e(t)} \cdot {r^{\prime}(t)}}{T \cdot {Z_{L}(t)}}{dt}}}}\ } & (2) \\{E = {\int_{0}^{T}{\frac{{p(t)} \cdot {r^{\prime}(t)}}{T \cdot {Z_{L}(t)}}{dt}}}} & (3) \\{E = {\int_{0}^{T}{\frac{{r^{\prime}(t)} \cdot {r^{\prime}(t)}}{T \cdot {Z_{L}(t)}}{dt}}}} & (4)\end{matrix}$

where E denotes the output power on line 226, P denotes the output poweron line 212, R denotes the output power on line 220, and Z_(L)(t)denotes the load provided by the element connected to line 220. Here theload may be both complex and active, resulting in a component of currentindependent of the voltage supplied.

The ratio of the output power supplied on line 220 to the powersrequired to generate the signals on lines 212 and 216 leads to anoverall supply efficiency expression of:

$\begin{matrix}{\xi_{out} = \frac{R}{\left( {\frac{P}{\xi_{p}} + \frac{E}{\xi_{e}}} \right)}} & (5)\end{matrix}$

where ξ_(out) denotes the output efficiency at line 220, ξ_(p) denotesthe efficiency generating line 212, and ξ_(e) denoted the efficiencygenerating line 226.

It is possible to express the overall efficiency in terms of therelative energy provided by an active correction element (such aselement 208) versus the energy provided by the high efficiency variablesupply 204, to provide a parameter k, such that k=E/P, as follows:

$\begin{matrix}{\xi_{out} = \frac{\xi_{p} \cdot \xi_{e} \cdot \left( {1 + k} \right)}{\left( {{k \cdot \xi_{p}} + \xi_{p}} \right)}} & (6)\end{matrix}$

From this expression it is observed that by ensuring k is much less than1, the resulting supply efficiency is dominated by the high efficiencyvariable supply block 204. The high efficiency variable supply block 204being made dominant, allows the efficiency of that supply to dictate theoverall efficiency of the supply architecture, and allows the efficiencyof the active supply correction block (such as block 208), generatingthe error or correction signal, to be of less importance.

This relationship is further illustrated in FIG. 4. For a fixed highefficiency supply having an efficiency ξ_(p), a trade off may beobserved between the error power ratio parameter, k, (i.e. the ratio ofthe error power E to the intermediate power P) and the requiredefficiency ξ_(e) of the active correction element 208.

Shown in FIG. 4 are plots of output efficiency (ξ_(out)) against errorpower ratio (k) for three different correction supply efficiencies. Plot406 represents a correction supply efficiency (ξ_(out)) of 0.5; plot 404represents a correction supply efficiency (ξ_(out)) of 0.6; and plot 402represents a correction supply efficiency (ξ_(out)) of 0.7.

In an envelope tracking or envelope elimination and restoration systemit is preferable for the resulting supply efficiency, ξ_(out), to begreater than 0.70. This typically corresponds to a supply configurationhaving parameters in the preferable ranges: ξ_(p)>0.7 (70%), k<0.4 (40%)and ξ_(e)>0.4 (40%). In an embodiment, for k, a still preferred range isk<0.3 (30%).

Hereinabove it is discussed, with reference to equation (6), that byensuring k is much less than 1 the intermediate supply voltageefficiency dominates the output efficiency. From equation (6) it is alsoapparent that to generally maximise efficiency it is desirable tomaximise both ξ_(p) and ξ_(e), while minimising k. Such a simpleoptimisation of (6) will, however, ignore the effect that maximisingξ_(p) and minimising k may have on ξ_(e).

For example, an optimisation method may provide a high efficiency supply204 and adaptation (correction) arrangement 208 which maximises ξ_(p)and minimises k at the expense of providing an error signalcharacteristic having a very high peak to average ratio and slew rate.In the extreme the error signal characteristics may exceed those of theoutput waveform. Such characteristics may result in a very low ξ_(e)efficiency and may result in an adjustment/correction means which isimpractical to implement, thereby adversely affecting the overallefficiency_(out)

It is thus preferable to optimise equation (6) to maximise the outputefficiency of the high efficiency variable supply 204, whilstmaintaining a joint objective of achieving a low peak-to-average ratiofor the error signal characteristics and a low slew rate for the errorsignal characteristics.

Preferably the high efficiency variable supply has sufficient trackingaccuracy to ensure that the ratio of peak error signal to peak outputsignal is less than 0.7. It is further desirable that the highefficiency variable supply has sufficient tracking accuracy to ensurethat the ratio of peak error signal slew rate to peak output signal slewrate is less than 1.5. Such ratios may reflect energy ratios or voltageratios.

In the absence of distortion the product of maximum slew rate and peakoutput may be directly related to the maximum bandwidth of the errorsignal. This optimisation suggests that both the high efficiencyvariable supply and the correction means preferably have similar outputbandwidths that are commensurate with, or moderately exceed, the desiredoutput supply characteristics.

From this analysis it may be determined that the active supplycorrection block 208 is preferably both substantially linear andachieves a medium level of efficiency with an error level signal havinga moderate peak to average characteristic and peak slew ratecommensurate with the output signal.

In the preferred implementation, the active supply correction block 208switches between a plurality of supplies in response to the outputrequired at the output on line 226, with the objective of maximising theefficiency in generating said signal. A preferred implementation of theactive supply correction block 208 is as a linear class G amplifier thatswitches between multiple supplies for efficiency.

In an alternative implementation the input supply to the active supplycorrection block 208 may be selected by an external element, such as forexample the tracking control block 206, based on knowledge of thecorrection required on line 226 or a prediction of such correction. Anexample implementation of the active supply correction block 208 in suchan arrangement is as a linear class H amplifier that switches betweenmultiple supplies for efficiency.

The scope of efficiency improvement to the active correction elementneed not be limited to a fixed supply switching Class-G or Class-Hoperation. Efficiency enhancement through continuous supply modulationtechniques, for example, may be provided.

Using a high efficiency supply for coarse tracking in combination with amedium efficiency supply for fine correction, results in a trackingsupply of substantial accuracy and efficiency.

A specific implementation of a supply architecture to achieve theinventive effects may be obtained in a number of ways.

Either one or multiple feedback loops be employed in controlling thehigh efficiency supply and correction elements to ensure that the outputsupply voltage level r′(t) on line 220 is a substantially accuratereplica of the tracking input r(t) on line 216. The architecture ofthese loops may be either joint or independent, and nested or spanning.

In an embodiment respective independent tracking loops are employed onthe high efficiency supply and the correction elements, with the formerdetecting the high efficiency supply prior to summing and the latterdetecting the final output post-summing. An example of such animplementation is illustrated in FIG. 5. Where elements of FIG. 5correspond to those shown in FIG. 2, like reference numerals are used.

As shown in FIG. 5, the tracking control block 206 includes a supplycontrol block 502, a delay block 504, and a combiner 506. The inputreference signal on line 116 is provided as inputs to the supply controlblock 502 and the delay block 504. An output of the delay block on line508 forms a first input to the combiner 506. A second input to thesummer 506 is provided by a feedback signal; on line 218 from the outputof the combiner 222, being the output supply voltage level. The outputof the combiner 506 forms the input to the active supply correctionblock on line 214.

In operation, the supply control block is adapted to provide thenecessary signal to the high efficiency variable supply block 204 toenable correct operation thereof. The supply control block 502 may, forexample, be an envelope detector, which provides an envelope waveform online 210. The supply control block may optionally receive feedback fromthe output of the high efficiency variable supply block on line 224.

The combiner 506 operates to combine the output supply voltage level online 220 with the delayed reference signal level, or idealised voltagesignal level, on line 508. The output on line 214 then represents thedifference between the two, being the error signal. The delay element504 merely ensures synchronisation of the signals in the architecture.

In another embodiment the feedback loop architecture may be substitutedfor feedforward, or a combination of both feedback and feed-forwardtopologies applied. An application of feedforward is illustrated in FIG.6. Where elements of FIG. 6 correspond to those shown in FIG. 2, likereference numerals are used.

A combiner 602 is provided, having a first input connected to receivethe reference input signal on line 116, and a second input connected toreceive the intermediate supply voltage level on line 212. The output ofthe combiner 604 forms an input on line 604 to the active supplycorrection block.

In this feedforward arrangement, it can be seen that the output of thecombiner represents the error in the intermediate supply voltage leveland the reference voltage level, which error can be used by the activesupply correction block 208 to provide the error signal on line 226.

Where a signal or control path exists, the implementation may includesuch delay elements as required to balance intrinsic delays withininterconnect, component and processing elements. The design andimplementation of such will be within the scope of one skilled in theart.

It is further anticipated that the tracking control element may employprediction to reduce or balance the overall delays between elements ofthe invention.

The invention has been described herein by way of reference toparticular preferred embodiments. However the invention is not limitedto such embodiments. The present invention may be advantageouslyutilised in any environment where variable or switched, selectablevoltage supplies are provided, but finds particular utility in theprovision of a power supply to a radio frequency amplifier.

What is claimed is:
 1. A power supply stage, comprising: generatingmeans configured to generate a power supply voltage from a highefficiency variable voltage supply based on a reference signal; andadjusting means configured to receive the generated power supply voltageand adapted to provide an adjusted generated power supply voltagetracking the reference signal.
 2. A power supply stage according toclaim 1, wherein an output efficiency of the high efficiency variablevoltage supply is greater than 0.7.
 3. A power supply stage according toclaim 2, further comprising a lower efficiency voltage supply forsupplying the adjusting means.
 4. A power supply stage according toclaim 1, wherein an output efficiency of the adjusting means is greaterthan 0.4.
 5. A power supply stage according to claim 1, wherein thereference signal comprises an input waveform representing a desiredsupply voltage level.